Methods and devices for bit-width control for bi-directional optical flow

A computing device comprising:

• one or more processors;
• and
• a memory with instructions for decoding a video signal stored thereon, the instructions, upon execution by the one or more processor, causing the computing device to:
• obtain a first reference picture and a second reference picture associated with a video sub-block, wherein the first reference picture is before a current picture and the second reference picture is after the current picture in a display order;
• obtain first prediction samples I(0) for samples in the video sub-block from the first reference picture;
• obtain second prediction samples I(1) for the samples in the video sub-block from the second reference picture;
• obtain motion refinements for the samples in the video sub-block based on a local window being applied to the video sub-block, by controlling bit-widths of intermediate parameters, wherein the intermediate parameters comprise one or a combination of following parameters:
• horizontal gradients, vertical gradients, and sample differences based on the first prediction samples I(0) and the second prediction samples I(1);
• and
• obtain bi-prediction samples of the samples in the video sub-block based on the motion refinements.

A non-transitory computer-readable storage medium storing instructions for decoding a video signal, the instructions, upon execution by a processor, causing the processor to:

• obtain a first reference picture and a second reference picture associated with a video sub-block, wherein the first reference picture is before a current picture and the second reference picture is after the current picture in a display order;
• obtain first prediction samples I(0) for samples in the video sub-block from the first reference picture;
• obtain second prediction samples I(1) for the samples in the video sub-block from the second reference picture;
• obtain motion refinements for the samples in the video sub-block based on a local window being applied to the video sub-block, by controlling bit-widths of intermediate parameters, wherein the intermediate parameters comprise one or a combination of following parameters:
• horizontal gradients, vertical gradients, and sample differences based on the first prediction samples I(0) and the second prediction samples I(1);
• and
• obtain bi-prediction samples of the samples in the video sub-block based on the motion refinements.